A primer on qualitative valence bond theory - a theory coming of age

The use of valence bond (VB) theory as a general and wide-ranging qualitative matrix of ideas and predictions is highlighted. Applications are demonstrated for chemical reactivity, properties of polyradicals, excited states, and chemical bonding. Highlighted subtopics include estimations of reaction barriers from simple properties of reactants and products; predictions of stable intermediates in organic, inorganic, and organometallic reactions; and predictions of reaction stereoselectivity. Additional coverage includes a pictorial model for ground and excited states of polyenes and polyradicals, predictions of Hund's rule violations, spin density polarizations and shifts, and a bonding rule in excited states of conjugated molecules. Discussion of new bonding ideas shows the far-reaching prospects of qualitative VB theory. C (C) 2011 John Wiley & Sons, Ltd. WIREs Comput Mol Sci 2011 1 18-29 DOI: 10.1002/wcms.7